A solid-state imaging device including effective pixels for outputting a signal based on photoelectric conversion, and reference pixels for outputting a reference signal without performing photoelectric conversion, is known. Such a solid-state imaging device obtains a difference between a signal output from effective pixels and a signal output from reference pixels to reduce noise in the output signal of the solid-state imaging device.
Although the pixel size in the solid-state imaging device is currently being miniaturized to improve resolution, the pixel size miniaturization reduces the area of a photoelectric conversion unit, degrading the sensitivity of the solid-state imaging device. Accordingly, with the solid-state imaging device, there has been a demand for simultaneously achieving high resolution and sensitivity degradation prevention by miniaturizing the pixel size while preventing the reduction in area of the photoelectric conversion unit.
Japanese Patent Application Laid-Open No. 2008-271280 discusses a solid-state imaging device including a plurality of effective pixels, reference pixels having equivalent characteristics to effective pixels except that photoelectric conversion is not performed, and differential pairs formed of effective and reference pixels, and correlated double sampling (hereinafter referred to as CDS) is performed.
An effective pixel includes a floating diffusion capacitance Cfd, which is connected to the gate of an amplification metal oxide semiconductor (MOS) transistor, for storing a charge output by the photoelectric conversion unit. A reference pixel is also provided with a floating diffusion capacitance Cfd connected to the gate of an amplification MOS transistor.
Each of the effective pixel and the reference pixel includes a capacitance Cio. One terminal of the capacitance Cio is connected to the output portion of a differential pair, and the other terminal thereof is connected to the gate of the amplification MOS transistor. With the configuration discussed in Japanese Patent Application Laid-Open No. 2008-271280, the capacitance value of the capacitance Cio is much smaller than the capacitance value of the floating diffusion capacitance Cfd. Hereinbelow, the capacitance Cio is referred to as micro capacitance Cio.
The solid-state imaging device including differential pairs formed of effective and reference pixels discussed in Japanese Patent Application Laid-Open No. 2008-271280 is capable of preventing both reset noise and fixed pattern noise contained in signals output from effective and reference pixels.
Japanese Patent Application Laid-Open No. 2008-271280 discusses a circuit configuration with which differential pairs are formed of effective and reference pixels, and amplification MOS transistors included in effective and reference pixels operate as MOS transistors of input stages of differential pairs. With the conventional configuration, there has been a problem that a defective reference pixel degrades the accuracy of a reference signal, resulting in degraded accuracy of signals output from a relevant differential pair.